1. Field of the Invention
The present invention relates to an anti-rotation lock device for preventing relative movement of a screwed assembly. The invention also relates to a screwed assembly including such an anti-rotation lock device. The invention also relates to the use of such an assembly in aircraft manufacture. The invention thus relates to the field of mechanical components for screwed assembly, in particular in the field of aircraft manufacture.
2. Description of the Related Art
In the prior art, a known anti-rotation lock device serves to keep a screwed assembly together and to prevent it from coming unscrewed in untimely manner, e.g. under the effect of vibration. FIG. 1 shows a prior art screwed assembly in the loose position, the assembly being of the kind used in the field of aircraft manufacture and comprising a prior art lock device for preventing said assembly coming unscrewed. The assembly comprises a rod big end for use in aircraft manufacture and forming an endpiece 110, a tube-forming rod body 100, together with a lock device 1 and a nut 180. The endpiece 110 is provided with a threaded shank 111 that can be screwed into a corresponding thread in the tube 100 and on which the nut 180 is tightened.
The lock device 1 comprises a first washer 120, a second washer 140, and a lockwire (not shown). The washers 120 and 140 are engaged on the threaded shank 111 between the tube 100 and the nut 180. The washer 120 has two catches on its face that faces towards the tube 100, one of which can be seen in FIG. 1 with the reference 123. The catch 123 co-operates with a notch 103 situated at the end of the tube 100, thereby enabling the washer 120 to be prevented from turning relative to the tube 100. The faces of the washers 120 and 140 that are to come into contact after the lock device has been tightened have complementary serrations that form a corresponding number of means for mutually locking the washers 120 and 140 against rotation.
The inner periphery of the second washer 140 is provided with a key 143 that penetrates into a longitudinal groove 113 formed along the threaded shank 111. The washer 140 is thus prevented from turning relative to the threaded shank 111.
After the nut 180 has been tightened onto the threaded shank 111, the nut 180 and the washers 120 and 140 are compressed against the tube 100, and the washers 120 and 140 are mutually locked against rotation by their serrations interfitting.
The outer periphery of the first washer 120 has a lug 125 pierced by a hole 126. The nut 180 has three holes 181, 182, and 183 that are pierced in directions that are substantially circumferential. To lock the nut against coming unscrewed, and thus ensure that the assembly remains cohesive, an operator needs to pass a lockwire through the holes 126 and 181 to 183, and then tension the lockwire by twisting its strands together. The lockwire thus maintains contact between the nut, the washers, and the tube.
Nevertheless, such an assembly is relatively lengthy to achieve, in particular because the operator needs to thread the lockwire through the holes. In addition, there is a risk of error in the direction in which the lockwire is installed, since the pitch of the thread may be left-handed or right-handed. Furthermore, the quality of the locking against rotation as provided by the lockwire depends on the tension given to the lockwire by the operator; if the operator does not tighten the lockwire sufficiently, then the nut and thus the lock device can loosen to a certain extent.
In addition, such an assembly requires a nut that is specific, given that it is pierced, thereby increasing costs. Furthermore, the twisted ends of the lockwire can injure an operator or catch on the operator's protective garments, and that is unacceptable in certain aircraft applications.